(1) Field of the Invention
The present invention relates to a charger for use in an image forming apparatus using an electrophotographic system, in particular relating to a charger having a structure that enables easy assembly as well as to an image forming apparatus including this charger.
(2) Description of the Prior Art
As is well known, an image forming apparatus using an electrophotographic system is comprised of processing portions for charging, exposure, development, transfer, separation, cleaning and charge erasure. Illustratively, for the step for recording an image, while an image bearer as a recording medium formed on a conductive support member made of, for example an aluminum drum, is rotationally driven, the image bearer surface is uniformly charged by the charger first. Then, the thus charged image bearer surface is illuminated with a light image of an original image via an optical exposure unit to record an electrostatic latent image corresponding to the light image. Subsequently, the electrostatic latent image on this image bearer is electrostatically adhered with toner for development to form a toner image on the image bearer surface.
Then, the toner image formed on the image bearer surface is transferred to a printing medium by a transfer device. The toner image transferred to the printing medium is fixed thereto by means of a heating and fixing device. The toner left over on the image bearer surface after transfer is removed by a cleaning unit and collected into a predetermined collecting portion while the residual charge on the image bearer surface after cleaning is erased by a charge erasing device in preparation for subsequent image forming.
The charger that is built in the image forming apparatus constructed as above plays an important role for uniformly charging the surface of the image bearer. However, there has been an assembly problem with the charger. Specifically, in the conventional charger, the engaging part for a discharge control electrode (grid electrode) and the part for applying tension to the grid electrode are provided separately, so that there is the problem that, that number of parts is increased and the assembly of these parts requires much time and labor. There is also a problem that it may be difficult to apply stable and desired tension so that the grid electrode will not slack when the grid electrode is assembled and disassembled.
To deal with this, the technology described in patent document 1 (Japanese Patent Application Laid-open H04-287061) discloses a mechanism to solve the above problems, in which one end of the grid electrode is fixed to one supporting member by means of a fixing member while the other end on the opposite side is engaged with an engaging member that is rotatably attached to another supporting member to thereby apply stable and desired tension to the grid electrode. This mechanism makes it possible by means of the engaging member to separate the work of attaching the grid electrode to the main shield case and the work for applying tension so as to facilitate the assembly work as well as to enable application of the necessary and stable tension.
However, even with the technology described in the above patent document 1, it was necessary to perform attachment of the discharge electrode inside the shield case and thereafter perform the attachment work of the grid electrode and the application work of tension. That is, it was impossible to shorten the working process, and the assembly needed dedicated attachment parts etc., for the grid electrode.